What makes that fresh rain smell? MIT films rain drops to find out

Why do we smell that fresh earthy scent before and/or after it rains? With high-speed cameras, MIT researchers have filmed rain drops, and believe that the footage explains petrichor, the “pleasant smell that frequently accompanies the first rain after a long period of warm, dry weather.” From MIT.edu:

Using high-speed cameras, the researchers observed that when a raindrop hits a porous surface, it traps tiny air bubbles at the point of contact. As in a glass of champagne, the bubbles then shoot upward, ultimately bursting from the drop in a fizz of aerosols.

The team was also able to predict the amount of aerosols released, based on the velocity of the raindrop and the permeability of the contact surface.

The researchers suspect that in natural environments, aerosols may carry aromatic elements, along with bacteria and viruses stored in soil. These aerosols may be released during light or moderate rainfall, and then spread via gusts of wind.

Suddenly the rain has additional dimensions. What else is in that fresh rain smell? According to Live Science in 2013, plant oils, actinomycetes, and ozone (which smells similar to chlorine) might also contribute.

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